1. Field of the Invention
This invention relates to a directional dynamic microphone, more particularly to a directional dynamic microphone which is interchangeable to have unidirectional and superdirectional characteristics.
2. Description of the Related Art
Referring to FIG. 1, a conventional directional dynamic microphone is shown to include a main body 4 with a magnet 401 and an iron yoke 402, a washer 5, a plastic outer ring 6 with a connecting plate 601, a rear cap 7 with through holes 702 formed therearound, a voice coil 2, a diaphragm 3, a protective cover 1, and a housing 8. A felt piece 703, a washer 704 and screw rod 705 are disposed between the rear cap 7 and the housing 8. A sound pressure regulating rod 9 passes through a through hole 802 in the housing 8 and extends forwardly to engage threadedly the screw rod 705 for securing the housing 8 to the rear cap 7.
By virtue of the through holes 702, the conventional microphone has a unidirectional characteristic. It is desirable for the microphone to have unidirectional and superdirectional characteristics so as to be adapted for use in different application.
The object of the present invention is to provide a directional dynamic microphone which is interchangeable to have unidirectional and superdirectional characteristics.
According to this invention, the directional dynamic microphone includes a protective cover with a front air-permeable major wall and a rear air-impermeable annular wall extending rearwardly from a periphery of the front air-permeable major wall around an axial direction. A diaphragm is in air-tight engagement with an inner proximate annular portion of the annular wall. A voice coil has a front looped section which is secured to a rear major side of the diaphragm, a rear looped section which is movable with the diaphragm in the axial direction, and two terminal ends adapted to be led out for transmission of an electrical signal. A magnet is disposed rearwardly of the diaphragm, and includes a core pole member and a tubular pole member of a polar nature opposite to that of the core pole member. The tubular pole member has a cylindrical portion which is spaced apart from the core pole member in radial directions such that an annular clearance is formed therebetween to accommodate the movement of the rear looped section so as to result in the electrical signal that is to be led out by the terminal ends.
An outer circumferential wall of the magnet includes an outer front circumferential portion which is spaced apart from an inner distal annular portion of the annular wall in the radial directions to confine a sound passage therebetween, an outer rear circumferential portion distal to the inner distal annular portion, and an outer intermediate circumferential portion between the outer front and rear circumferential portions. The outer intermediate circumferential portion engages the inner distal annular portion, and has a sound port that opens outwardly and radially for air communication with the sound passage. The outer rear circumferential portion has a plurality of sound holes which are angularly displaced therein around the axial direction. Each sound hole is of a dimension smaller than that of the sound port, and extends inwardly and radially for air communication with the rear major side of the diaphragm. A phase shift effecting sheet is made of a flexible material, and veils the sound port so as to impart the dynamic microphone with a unidirectional characteristic. By virtue of the sound holes, the dynamic microphone is superdirectional. A cylindrical shield member is sleeved on and is retainingly slidable relative to the outer rear circumferential portion around the axial direction, and has a plurality of through holes which are angularly displaced therein around the axial direction. As such, when the cylindrical shield member slides angularly relative to the outer rear circumferential portion to a unidirectional position, each through hole is not registered with a corresponding sound hole so that a sound wave is denied entrance into the sound holes to maintain the unidirectional characteristic of the dynamic microphone. When the cylindrical shield member moves to a superdirectional position, each through hole is registered with the corresponding sound hole so as to admit the sound wave thereinto and impart the dynamic microphone with the superdirectional characteristic.